1. Field of the Invention
This invention relates to electric switching devices, and more particularly to electrical switch units that incorporate a plunger-type actuator in order to effect the make and break operations. The invention is considered to have special utility in the automotive field, where typical switch devices are subjected to extremes of temperature, humidity, mechanical shock and rough handling, and yet are expected to operate satisfactorily over extended periods of time.
2. Description of the Related Art including information disclosed under 37 CRF .sctn..sctn.1.97-1.99
In the past numerous push-button type electric switches have been proposed and produced, meeting with varying degrees of success. Many such devices were employed in automotive vehicles in conjunction with the vehicle's doors, being installed in the door jamb in order to operate courtesy lights, etc. Still others found wide acceptance for use with the vehicle's hood and trunk compartments, in order to indicate various conditions, such as when the hood was not fully latched, or for triggering alarm circuitry if unauthorized entry into the vehicle was attempted.
Frequently these switches were simple make-and-break devices having normally closed circuits, with the contacting surfaces at least partially exposed. Under such circumstances there was a tendency for moisture, salt, dirt and sand or other debris to become lodged in the switch mechanism, causing either erratic operation, deterioration, or eventual failure. Efforts to prevent the accumulation of such matter by means of sealed switch casings, have not led to much commercial success for the reason that the expense involved in providing an effective seal was not warranted, despite the multiple units that were employed on newer model vehicles. Yet it was considered important that such switches be reliable in operation, and not subject to breakdown under the extreme environmental conditions to which vehicles are typically subjected. Compromise constructions in general left something to be desired, considering the objectives of economy and useful life under adverse operating conditions.
Manual operation of plunger-type switches normally presents few problems as regards the extent of movement of the plunger, or the forces intended to be applied to the plunger. That is, the operator merely depresses the plunger or push button with a moderate force, until the desired circuit is energized or otherwise affected. However, with plunger-type switches that are intended to be automatically actuated by engagement of the switch plunger by a relatively massive member, such as the hood, trunk lid, or door of a vehicle, there arise problems in insuring that the physical dimensions and tolerances of the switch are in accord with the space requirements dictated by the particular application. Specifically it is necessary to insure that the plunger is not subjected to excessive force or impulses, since this could result in permanent damage to either the plunger, the switch housing, or the contact mechanism in the housing.
Also, where a massive object such as an automobile hood is moved, the resulting inertia can give rise to a considerable overtravel, often followed by a re-bound or backing-off. Prior switches have, for the most part, been unusable in such installations, due to the impulse forces applied to the switch plunger, and the adverse effects of such overtravel on the movement of the plunger.
Accordingly there has existed a long-felt need for a sturdy and reliable inexpensive switch which would perform satisfactorily under the circumstances noted above, and which would eliminate the problems that often plagued many of the prior switch arrangements.